Script based default value for integer

So I thought I was trying something simple but somewhere I obviously went wrong.

What I want is set an attribute to a default value (tried any number but want work item ID actually)

- I created a script based default value and used the example, only changing the return value to an actual number during my tests
- switched to "types and attributes" and set the default value to the script based value

saved and tried and - nothing! it simply doesn't react! When trying to debug it, it doesn't even seem to use the default value at all.

the process configuration says I have the value provider set so I'm really not even sure where to start to look why this doesn't work. If I use a simple number default value everything works fine.